This invention relates generally to a golf club shaft, and in particular to a golf club shaft that has improved playing characteristics.
A golf club shaft may normally be made of different types of material, such as wood, metal or a composite material, and be tapered to have a smaller diameter lower portion with a tip end that is connected to a golf club head, and a larger diameter upper grip or butt portion where a player grips the shaft.
Golf club shafts have several physical characteristics that determine the playing characteristics of the shaft, including a flex point and stiffness. The flex point of a golf club shaft is the point at which the shaft has its maximum deflection when flexed. It may be determined by clamping both ends of the shaft so that neither end can move, and then flexing the shaft. The location where the greatest deflection of the shaft occurs is known as the flex point, which is also known as the kick point. The location of the flex point determines the trajectory that a golf ball may have when struck by the golf club as well as the speed of the golf ball. Typically, beginning players desire a higher trajectory so that they want a golf club shaft with a lower kick point. Professional players, who have sufficient strength and skill to drive a golf ball without added trajectory, want a lower flight and a golf club shaft with a higher flex point. The flex point depends on the structure and material of the shaft. For example, a shaft with a constant diameter will have a flex point located at its midpoint, whereas a tapered shaft will have its flex point located more towards the small end of the shaft. The flex point may also be changed by changing the material of the shaft.
The stiffness of a shaft also affects the playing characteristics of the shaft. The stiffness of the shaft depends on the diameter of the shaft, the material from which it is made and to a lesser degree the wall thickness. For example, a constant diameter shaft would have a constant stiffness, but a tapered shaft would have different stiffness at different parts of the shaft. Typically, a professional player that may swing a golf club with a velocity of about 100 mph wants a stiffer shaft because a more flexible shaft bends too much. A beginning player needs a more flexible shaft because the beginning player cannot swing the golf club with as much velocity as a professional player.
Typical golf club shafts may have a taper that is constant from the upper grip or butt end down to the lower tip end. Thus, the diameter of the shaft is constantly increasing to a maximum diameter at the upper grip end of the shaft. This conventional constant taper golf club shaft is easy to fabricate. However, due to the constant taper, the shaft has a smaller diameter tip end that may be less stable and more flexible than the thicker upper portions such as the grip end section. The less stable tip end has a number of drawbacks that affect the overall playing characteristics of a golf club. First, since the tip end is more flexible, it has less rigidity and the tip end of the shaft tends to twist and bend when loads are exerted on it. In particular, when a golf club is swung, the torque forces acting on the heavy club head tend to twist the tip end of the shaft causing the club head to unsquare and strike the golf ball at an angle, leading to inaccurate golf shots. Second, as the golf club head strikes the golf ball, a force is exerted on the golf club head by the golf ball, which also may tend to bend the tip end of the shaft and unsquare the club head. Third, the more flexible shaft cannot support the weight of a golf club head and the head tends to droop which in turn causes the shaft to bend. Twisting and bending causes the club head face to strike the golf ball at an angle which leads to inaccurate golf shots. Thus, a conventional constant taper shaft may have a tip end that is not rigid enough to prevent the twisting and bending that may occur. Thus, this conventional club may have unsatisfactory playing characteristics.
To improve the playing characteristics of a golf club, some conventional golf club shafts have substituted various stronger composite materials in the tip end of the shaft in an effort to build up the sidewalls of the tip end. These composite materials, however, may be very expensive or difficult to work with. In addition, these composite materials may have only limited benefits because the tip end has a small diameter so that only a small amount of composite material may be added to the tip end of the shaft. Thus, using additional composite materials does not significantly improve the playing characteristics of a golf club.
Other conventional shafts may attempt to improve the playing characteristics of a golf club and the stability of the tip end of the shaft by increasing the overall diameter of the entire shaft or by employing shafts with varying diameters or tapers. An oversized diameter shaft may have a stiffer, more stable tip end, but it also has an oversized grip section that may be too large for most players. In addition, the oversized diameter shaft may be too heavy or too stiff so that it does not feel good to most golf players. Other conventional shafts may have non-constant tapers that improve the playing characteristics of the golf club, but these non-constant tapered shafts are expensive and are also more difficult to manufacture. These non-constant taper shafts may also be too heavy.
The stability of the golf club head is critical to the playing characteristics of a golf club and the stability is strongly influenced by the shaft characteristics. Varying the relationship between the lower tip end of the shaft and the upper grip section has not proved successful in the past. As the lower tip end may be stabilized to improve the strength of the tip end, the upper grip end must also be altered in order to have a golf club shaft that feels good to the golf player, and this combination has been difficult to achieve. None of the conventional golf club shafts have been able to achieve a stable tip section as well as a grip section that feels good to a golf player.
Thus, there is a need for a golf club shaft which avoids these and other problems of known devices, and it is to this end that the present invention is directed.